code: def test_TransformerLM_backward(pos_enc):
      model = TransformerLM(10, pos_enc=pos_enc, unit=10)
      input = torch.randint(0, 9, [2, 5])
  
      out, h = model(input, None)
      out, h = model(input, h)
      out.sum().backward()
  
file_path: espnet/test/espnet2/lm/test_transformer_lm.py
imports: import pytest
  import torch
  from espnet2.lm.transformer_lm import TransformerLM
  from espnet.nets.batch_beam_search import BatchBeamSearch
  from espnet.nets.beam_search import BeamSearch
label_desc: Use image node_id 1 for calling a global function with example usage: test_TransformerLM_backward(pos_enc) without return types